The literature provides evidence that tooth pain thresholds vary according to the parameters of stimulation, time of day, sex, age, emotional state etc. None of this previous work has attempted to define the tooth pain experience in terms of the pain perception threshold which is sensory and has a subjective end point, and the pain reaction threshold which is influenced by the emotional set of the subject. Additionally, the techniques whereby dental anesthesia is produced are numerous, while a comparison of the effects of the different methodologies on the dental pain threshold and response bias are virtually non-existent. In this study it is proposed to utilize signal detection (sensory decision) theory as a means of comparing tooth pain threshold changes and response bias shifts under the influence of local anesthesia, 33 per cent nitrous oxide or acupuncture analgesia. In addition, throughout the study, physiological variables such as pulse rate, respiration, blood pressure and pulpal blood flow (estimated by phototransmittance) will be compared with the response bias shifts and threshold changes.